IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specification for implementing wireless local area network (WLAN) computer communication in the Wi-Fi (2.4, 3.6, 5, and 60 GHz) frequency bands. The standards and amendments provide the basis for wireless network products using the Wi-Fi frequency bands. IEEE 802.11ah is a new wireless networking standard from the IEEE 802.11 wireless networking standard family. The purpose of IEEE 802.11ah is to create large groups of stations that cooperate to share air medium while minimizing energy consumption. Apart from the conventional ISM bands of 2.4 GHz and 5 GHz, IEEE 802.11ah is set to dive into the unlicensed 900 MHz band as the widespread usage of Wi-Fi in 2.4 GHz ISM band has led to contention problems. The most prominent aspect of IEEE 802.11ah is the behavior of stations that are grouped to minimize contention on the air media.
While 2.4 GHz Wi-Fi commonly uses three 20 MHz channels (in the available 85 MHz of spectrum), the 802.11ah standard uses a more restricted 902-928 MHz band (in the United States). In Japan, the available band is within 916.5-927.5 MHz, with eleven 1 MHz channels. In China, the available band will be within 755-787 MHz, with thirty-two 1 MHz channels. The new 802.11ah standard allows twenty-six 1 MHz channels or thirteen 2 MHz channels. The PHY transmission in IEEE 802.11ah is an OFDM waveform consisting of 64 tones/sub-carriers that are spaced by 31.25 kHz. The modulations supported in IEEE 802.11ah include BPSK, QPSK and 16 to 256 QAM. IEEE 802.11ah also supports multi user multiple-input and multiple-output (MU-MIMO) and single user beam forming.
The new IEEE 802.11ah standard aims at providing a long-range Wi-Fi transmission. In addition, the prime use is intended to be in wireless sensor networking owing to power saving strategies. The devices operating in IEEE 802.11ah mode are believed to have long battery life and long network reach due to the propagation characteristics at below 1 GHz sub gigahertz spectrum. IEEE 802.11ah uses IEEE 802.11a/g specification that is down sampled to provide the 26 channels, each of them able to provide 100 Kbit/s throughput.
In an IEEE 802.11 wireless communications system that provides both conventional Wi-Fi service and IEEE 802.11ah service, a long-range basic service set (BSS) has a coverage area radius of up to one kilometer, which is a multiple of that of a short-range BSS. A long-range BSS may enclose and overlap spatially with several short-range BSSs. The long-range BSS occupies a narrow 1 or 2 MHz channel, while the short-range BSSs each occupies a wide 8 MHz channel, consisting of four 2 MHz channels. Different stations (STAs) are associated with different access points (APs) providing wireless services. An overlapping station STAO is associated with a long-range APL that is also within the coverage of a short-range BSS. A long-range station STAL is associated with the long range APL that is not within the coverage of the short-range BSSs. A short-range station STAS is associated with a short-range APS that is also within the coverage of the long-range BSS. The APSs and STASs will hear the traffic of the long-range BSSs and set up collision avoidance scheme accordingly. However, some of the APLs and STALs may not hear the traffic inside some of the short-range BSSs and would not set up collision avoidance scheme accordingly. As a result, the traffic in the long-range BSS may collide with the traffic in some of the short-range BSSs and cause data loss.
A solution is sought.